NetNews Usenet Archive 1993 #3/NN_1993_3.iso/spool/bit/listserv/pagemakr/2375

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Subject:      Scanning FAQ Update Part 1 of 4
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-------------         PAGEMAKER/QUARK LISTSERV               -----------------
-------------   S C A N N I N G    F A Q    UPDATE 1/22/93   -----------------
Part 1 of 4

 Special Thanks...

 To Geof Peters, Monte Olsen, Cindy Stone, Gary Hartling, Jeff Needleman,
 and the guy who ask for a explanation of the meaning of life that gave
 me a deluge of new material to use in updating this FAQ.  Many of you will
 note your remarks incorporated into this FAQ without the slightest regard
 for crediting the source.

 Also my thanks to Pete Fink, the president of Peter Fink Communications (the
 guy who helped Adobe create Adobe Accurate Screening technology), and
 publisher of "Desktop to Press" newsletter for allowing me to use excerpts
 from his resource known as the "How to Make Sure What You See Is What You
 Get" booklet.

 We like it so much that we give it to all of our Service Bureau clients.

 Much of this FAQ is drawn from excepts of this resource, and I would like
 to give him full credit for allowing me to use his booklet as a springboard
 for this FAQ, for reasons of consistency, readability, and because I am
 plugging his booklet so thoroughly his office deemed it unnecessary to foot-
 note all occurrences of information taken directly from his work.  I recom-
 mend you contact him for a complete copy:

     Peter Fink Communications, Inc.
     120 Q Street NE
     Washington, DC  200002
     [phone]

 Get the booklet ($10.95 US plus shipping and handling, less in quantity),
 it goes on to cover Halftones and Dot Gain, Optimum LPI, Fonts, Cropping
 and Scaling, Masking and Flatness, Blends and Banding, and more all in a
 24 page booklet you can keep by your computer.

----------------------------------------------------------------------------

 Scanning artwork can be broken down into four primary catagories:

    1) Line Art
    2) Halftones
    3) Greyscale
    4) Color

    Each of these catagories have their own unique problems when scanning,
 before I continue with some techniques for greyscale scanning, I'd like
 to define and discuss these catagories.



 Line Art Scanning
 -----------------

    Line Art scanning is best defined as simply transferring pen and ink
 style drawings, clip art, and some pencil sketches into the computer
 system.  Line Art has no shading nor color other than black.  Line Art
 scanning is considered 1-bit scanning, that is the computer sees the
 image as either black or white.

    Line Art scans, since they can only be black or white, do not have the
 luxury of anti-aliasing (a technique that makes smooth transitions between
 black and white by adding varying steps of grey), and therefore are prone
 to having jagged edges around curves when scanned at lower resolutions
 than the final output device.  Therefore, you should not use Line Art style
 scanning to scan photographs or textured art unless you are attempting to
 achieve some special (read - often weird) effects.

    Line Art should be scanned at as high a resolution as the final output
 device to eliminate the "jaggie" effect. In other words if you have original
 art that is 5x7 and you're going to output at 5x7 on a 1200 dpi imagesetter,
 ideally it should be scanned at 1200dpi to achieve the best possible image.
 Note that if your original is larger than the final size, you should adjust
 your original scan resolution by the same ratio so as to not have more
 resolution than necessary.

    On a personal note here, while the goal of matching original scan
 resolution with final output resolution is desirable, very few of
 your clients will be able to discern any difference between 600dpi scans
 and 1200dpi scans, especially when your final output will be printed on
 glossy paper stock.  However, the difference in imaging time to your printer
 or imagesetter will be quite remarkable since you are dealing with 4 times
 as much data in a 1200dpi scan.

    Geoff Peters adds, One last thing worth mentioning here is tracing.
 The majority of line art that he scans are simple cartoon drawings or
doodles.
 He then uses Corel Trace to convert it to postscript and thus enables him to
 increase the image to any size with out the fear of the Jaggies.



 Halftone Scanning
 -----------------

    Halftone scanning evolved because someone discovered that they could
 scan photographs from magazines.  While I won't get into the legal issues
 here, suffice it to say that there will be a legal problem with using any
 pre-published images.  Assuming that you have the permission to use a
 pre-printed piece, don't -- ask for the original photograph instead.

    Halftone scanning is essentially treated like a greyscale scan by most
 software and the conventional wisdom says to scan the image at a
 resolution lower than the original in order to reduce the threat of
 moires.  Well, about all you can do is reduce the number of moire patterns
 that you will have, not reduce the threat.  If you scan a halftone, you
 will have moires.  Without  getting too technical, the reason for this is
 that all halftones generated by a press have "irrational" screens and
 inconsistent angles applied.  Irrational screens and inconsistent angles
 are used to increase the quality of the printed piece for the type of
 press being used, they are called irrational and inconsistent because in
 the case of the press, they are adjusted mechanically by the press
 operator (If they were generated by a high-end four-color system--Scitex,
 Chromacom, etc.--the irrational screens were computed elaborately).  To
 properly eliminate potential moires your scanner would have to adjust its
 resolution, tracking (pickup alignment), and linearity (the range of
 grey scales) dynamically across the entire image.

    Granted, this may not be a big deal if all you intend is to scan the
 cover of SI's swim-suit issue to embarrass your colleague (of course, I
 would never advocate this type of blatantly criminal activity), but
 assuming your goal is publication quality work, Halftone scanning should
 always be used as a last resort if at all.



 Halftone Scanning vs. Halftone Screening
 ----------------------------------------

    Halftone scanning should not be confused with halftone screening.  Sound
 confusing?  Halftone scanning is scanning an original from an already screen-
 ed source such as a magazine, coffee table book, newspaper, etc.  However,
 many scanners now come with plug-ins, or custom software that has an option
 labeled "Halftone."  Check your manual about this, but most of these options
 are for creating a custom halftone screen of the image being scanned not for
 scanning a pre-screened halftone.

    As an example, Microtek's Adobe PhotoShop plug-in has a halftone option
 that allows you to screen an image to a number of preset patterns as you scan
 the original.  This is important because Microtek, and most other scanner
 makers, have done their homework on their scanners and know how to generate
 a halftone screen that will best take advantage of their machine's capabili-
 ties with your chosen output device.  Another advantage is that once the scan
 is completed, you don't have a large grey scale file, but rather a simple
 1-bit black and white file that approximates the grey range of your selected
 output device and takes up only a fraction of the space that a grey scale
 would.

    The disadvantage to this, is that your screened scan is now appropriate
 for really only one output device.  For instance, If you perform a halftone
 scan with the Microtek plug-in set for a "5x5 60 dot #1" pattern (the recom-
 mended pattern for the Apple Laserwriter IIf photograde) it will look great
 when printed to the Laserwriter, but appear like a strange rippled newspaper
 photo when printed at 1200dpi on a Linotronic.

    Halftone screening a scan is not entirely without merit, however.  Many
 manufacturers will give you some screen patterns (such as horizontal or
 vertical lines) that can create some very artistic effects regardless of
 output device.


 Greyscale Scanning
 ------------------

    Greyscale scanning is most often used for original photographs, but can
 also be effective for maintaining the "soft" edge of some pencil sketches
 that use lots of shading.  Most good flatbed desktop greyscale scanners
 are now capable of scanning 256 shades of grey.  Don't be swayed by a
 manufacturers claim of 4096 shades of grey.  While this may be true, you
 won't be able to use them.  The current PostScript specification only
 allows for 254 halftone steps (the way a shade of grey is represented in
 print, 254 steps with pure white and pure black which makes 256 total).


    Principles

    Most of us scan at too high a resolution.  As we increase scan
 resolution, we capture too much detail--and the scan's file can balloon to
 outrageous size.  The imagesetter [ or laserprinter ] must render all of
 that data, using lots of costly RIP time [ RIP - Raster Image Processor,
 the specialized computer in your laserprinter or more expensive
 imagesetters.

    As you work with a scanned image, the computer constantly has to re-
 crunch the scan data.  Over the course of a project this time really adds
 up.  Scans with way too much data not only rob your time, they can even
 crash the RIP--in which case you don't even get a page.

    Take a few moments to calculate what you need rather than scanning at
 high detail "just to be on the safe side."  Capture just enough detail for
 what you need to do.

    Production Tips

 -   Do a little arithmetic before you scan.  Planning to reduce the image
     to 50%?  This doubles the resolution.  Reducing to 33% triples the
     resolution, and so on.

 -   For greyscales, a final resolution of 1.5 times the LPI works well in
     most cases.  For soft subjects you can get away with 1.3 times the
     LPI.

     (i.e. - Linotronic output at 1200 dpi, 133 lpi your scan resolution
              should be no greater than 200 dpi.  Final scan resolution
              means that you've calculated the change in spatial
              resolution when you size your original scan, as
              discussed in the above tip)

 -   Avoid data overkill.  Clean up scans in a retouching program before
     using them.  Adjust their size and resolution before placing them in
     a layout program.

     Crop the image in a package like PhotoShop or PhotoStyler as closely
     as possible to avoid having the RIP compute all that "white space."
     Avoid using PageMaker or other layout programs ability to "crop" a
     scan, this feature merely masks an area and does not decrease the
     data that the RIP must compute.

 -   Sharpening the image in a retouching program gives a better looking
     result than using a high scan resolution.  Make the on-screen image
     just a little sharper than you think is needed--it softens a bit in
     production.

     The CCD chip in your scanner that actually reads the greyscale data
     is linearily balanced, meaning that the transitions between grey
     areas tend to be minimized too much.  Sharpening algorithms in
     retouching programs like PhotoShop and PhotoStyler adjust for
     this.  Always run your programs "Sharpen" routine on a scanned
     photo to compensate for this.

     Another little known tip is to add "noise" to a scan to minimize
     the transitional steps between your grey scales.  For instance if
     you have created a blend in your illustration package that has only
     thirty steps, you can export the EPS file into your favourite image
     editor and add 1 or 2 units of random "noise" with the noise filter
     to take away hard edges and "cheat" your eye.  This technique works
     well for ultra-high and very low resolution scans too that either
     exceed the grey level of your imagesetter or produce very pixelated
     images.


    Common Mistakes

 -   Taking a big high resolution scan and shrinking it to tiny size--16
     Megabytes for a postage stamp--yow!  Reduce resolution by sampling
     down in a retouching program or re-scan at a lower resolution.

 -   Cropping a little piece of a big image in a page layout program--the
     RIP has to process that whole big image, then *throw away* what's
     outside the cropping window.  Crop first in a retouching program, and
     bring what you need of the image into the page at the proper size.

 -   Misuse of the text wrap feature of PageMaker. Be careful not to overlap
     your wrap points (ie - create a spider web of an irregular shaped text
     wrap where a wrap point is inside another wrap point, this mistake will
     crash the RIP because you are allowing PageMaker to define an illegal
     object (the object of the text wrap outline and associate it with the
     scan object)

 -   Thinking that white borders don't count--white creates data too.
     Crop the borders away while scanning to save the most time, or later
     in your image editing software.

 -   Using a page layout program to rotate big images.  The RIP likes its
     image data straight.  Twisting all those pixels is risky, lengthy
     work.  Rotate in a retouching program.

 -   Scanning Line Art as a grey scale because it has fancy stippled
     shadow detail.  Scan your artwork at a higher Line Art resolution
     rather than grey scale.  2x3 inch 150 dpi 8-bit grey scale is 2 Meg
     worth of data compared to 600K for a 2x3 inch 400 dpi 1-bit Line
     Art scan.



 Color Scanning
 --------------

    First, color scanning _is_ possible on the desktop regardless of what
 your stripper may have said.  And it would be possible for me to write a
 few thousand pages about how to not do it, but in this FAQ, I'm going to
 limit our discussion to primarily greyscale scanning.  But while I have
 your attention I may as well interject my opinion about color scanning.

    For most of us, color scanning is needed for color separations for used
 in four-color printing.  Your Howtek, Microtek, Sharp, or even Nikon color
 scanner does a good job if you have a skilled operator and an exacting
 output service bureau, but don't assume you are going to save any money or
 time. More often, the years of color experience a good four-color shop has
 is worth the effort to use traditional methods, and will save you time in
 the long run.  We have one of the best desktop color systems around
 (Quadra's with SuperMac displays, 128 Meg Memory, 2 Gigabyte Hard Drives,
 Nikon LS3510 slide scanner, and Optronics Colorgetter Drum Scanner System)
 and we choose not to use it for large format and high quality
 pieces.  We instead send these out to a local Chromacom-based Separator.

    If your bent on doing color on your desktop, try a hybrid approach.
 Traditional four-color separator scans the art and gives the DTPer a low-
 res image for placement.  Output is then sent back to the four color shop
 where the high res is used.  Hybrid methods are growing in popularity as
 users realize their "eye" for color and equipment isn't as good as expected.